Such nanocomposites can advantageously be used, for example, as cable insulation materials. PVC, used until now to sheath and insulate cables, must be replaced because of the toxic and corrosive products that can be released during combustion. However, the currently available non-halogenated fire-resistant materials are both expensive and have low resistance to heat and oil. Thus, a material is sought that is compatible with the environment and that does not have the disadvantages cited above, to replace PVC in insulating parts or in cable sheaths.
A further solution for rendering cable sheaths more fire-resistant is to add a large quantity of metal hydroxides. However, the mechanical and electrical properties of the cables degrade.
Nanocomposites are composite materials comprising sub-micronic particles dispersed in an organic matrix. In particular, lamellar inorganic materials such as graphite or silicates have the ability to intercalate organic compounds such as polymers between their lamellae. When the repulsive forces between the atoms of the organic compound exceed the attractive forces between the lamellae, the lamellar material delaminates, resulting in a hybrid structure in which the lamellae are dispersed through the organic compound matrix.
However, preparing nanocomposites generally necessitates pre-treating the lamellar material. In order for the organic compound, in general a polymer, to be able to penetrate between the lamellae, the lamellar material preferably presents an organophilic nature, which it generally does not normally possess. In that case, the surface of the inorganic material has to be pre-treated to endow it with that more organophilic nature.
International patent application WO-A-93/04117 describes nanocomposites obtained by treating the lamellar inorganic material with swelling/compatibilizing agents such as primary and secondary amines or quaternary phosphonium cation complexes with residues containing a certain number of aliphatic carbon atoms. Such long carbon chain compounds interact favorably with the intercalating compound. However, it has been shown that the thermal stability of clays treated with quaternary ammonium salts is lower. Further, ammonium salt decomposition can cause decolorization, the formation of gaseous products, and it can degrade mechanical properties.